MCCs are used in a number of industrial and commercial applications to house and interconnect motor control units via a common power bus. An MCC may be installed in a separate air-conditioned room or may be installed adjacent to a controlled motor or other equipment. An MCC may include one or more cabinet sections with the common power bus, and individual motor control units are plug-in mountable to the common power bus. MCCs may house variable frequency drives, programmable controllers, and metering, for example.
Arc flashes may result from faults at components within the MCC. An arc flash is the light and heat produced from the fault and may cause damage to surrounding equipment, fire or injury. The energy released in the fault blasts debris outward with a large force.
Depending on the demands of a customer, an arc-resistant MCC uses an expansion chamber (e.g., a pull box) with a pressure flap or a plenum duct assembly to vent the products of the arc flash out of the MCC. The expansion chamber with the pressure flap vents the products of the arc flash to the immediate vicinity of the MCC and/or the motor controlled. The plenum duct assembly carries the products of the arc flash to a location away from the MCC and/or the motor controlled.
The arc-resistant MCC is provided with either the expansion chamber or the plenum. Arc flashes create pressure. Different arc-resistant MCC bases are used depending on whether the expansion chamber or the plenum is to be attached, as the expansion chamber and the plenum deal with the created pressure in different ways and are accordingly attached to the MCC base in different ways. This results in stocking a number of different bases.